A cellulose nanofiber which has been developed in recent years is a natural material nanofiller derived from a plant and is noted as a low-specific gravity and high-strength composite material for a resin.
However, in order to fibrillate cellulose having many hydroxyl groups up to a nano-level, it is necessary to be fibrillated in water or to be fibrillated by mixing a resin with large amounts of water according to the technology at present. Therefore, cellulose nanofibers after fibrillation contain water to a great extent (refer to PTL 1). In the case where the resulting fibrillated cellulose nanofibers containing water are dispersed into various resins, a step to dehydrate the produced cellulose nanofibers is necessary. Meanwhile, cellulose forms an intermolecular hydrogen bond easily and, therefore, the cellulose nanofibers are re-flocculated during the dehydration step, so that dispersion in the resin is poor.
In order to solve these problems, a technology to produce cellulose nanofibers by fibrillating cellulose not in water, but in an organic solvent has been reported (refer to PTL 2). It is disclosed that, according to this technology, dehydration steps are not necessary so that cost of dispersion of nano fibers into resin is more competitive. However, combination with the resin requires steps to disperse in the organic solvent up to a nano-level initially and, then, remove the organic solvent. Therefore, it is not said that complicated production steps of the nanofibers have been improved.
That is, establishment of a technology capable of combining cellulose nanofibers with various resins through more inexpensive and simple steps has been required.